User-defined routing tables not created for loopback interface

[Nicholas Schell]

Ubuntu: 20.04.2 LTS
netplan.io: 0.101-0ubuntu3~20.04.2

Attempting to use the following config:

network:
    version: 2
    ethernets:
        loop0:
            match:
                name: lo
            routes:
                - to: 0.0.0.0/0
                  via: 127.0.0.1
                  table: 99
            routing-policy:
                - to: 0.0.0.0/0
                  mark: 7
                  table: 99

Will create the rule, but not table 99.

root@ubuntu-focal:~# ip rule list
0: from all lookup local
0: from all fwmark 0x7 lookup 99
32766: from all lookup main
32767: from all lookup default

root@ubuntu-focal:~# ip route show table 99
--- no output ----

However using the same config on Ubuntu 18.04 is working.
Ubuntu: 18.04.5 LTS
netplan.io: 0.99-0ubuntu3~18.04.4

root@ubuntu-bionic:~# ip route show table 99
default via 127.0.0.1 dev lo proto static

The generated configs in /run/systemd/network/ is the same on both systems.

root@ubuntu-focal:~# cat /run/systemd/network/10-netplan-loop0.network
[Match]
Name=lo

[Network]
LinkLocalAddressing=ipv6

[Route]
Destination=0.0.0.0/0
Gateway=127.0.0.1
Table=99

[RoutingPolicyRule]
To=0.0.0.0/0
Table=99
FirewallMark=7

This seems very similar to this report: https://bugs.launchpad.net/ubuntu/+source/netplan.io/+bug/1830641
Except that my config is working on Ubuntu 18.04, and I'm not dealing with any DHCP related routes since this is the loopback interface. Is there a new configure option or something I'm missing from a change in Ubuntu 20.04? Or some change to networkd possibly?

[Nicholas Schell (nschell)]

Also tried downgrading to the earliest package available in Ubuntu 20.04 (netplan.io: 0.99-0ubuntu1) with no change.

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Stephen Fletcher (mridion)]

Tried applying routing policy example from man file in Ubuntu 20.04 for a physical interface and have the same issue where the "ip route list <#>" shows nothing.

[Stephen Fletcher (mridion)]

I should note that the man example for "routing-policy" is using "NetworkManager" as the renderer but I am using the Ubuntu Server default "networkd" as the renderer. Not sure if "routing-policy" is simply not supported yet with using networkd as the renderer. Either way I get the same issue as the OP

[Stephen Fletcher (mridion)]

Doesn't seem to apply to my situation so removing myself from affected list.

[Nicholas Schell (nschell)]

What would be the most appropriate place to report the problem for networkd?
The launchpad seems completely dead: https://bugs.launchpad.net/ubuntu/+source/networkd-dispatcher